Existing tracking techniques such as GPS [1]}, [2]} and mobile phone data [3]}, [4]} are too coarse for such a task because social interactions often occur within 1-2 meters [5]}, beyond the spatial resolution of these traditional techniques. In addition, social events may take place indoors where GPS and cell phone tracking are largely limited to track social contacts. Badge-based technologies [6]}, [7]}, [8]}, [9]} and Bluetooth scanning [8]} allow detection of social contacts when two individuals are within a certain distance. However, badge-based technologies neither give an explicit description of the defined social distance nor capture the exact locations where interactions take place.
